US 20080257017 A1 Abstract A method and a system is disclosed for determining cetane values from constant volume combustion chamber apparatuses capable of producing pressure versus time combustion profiles having a fast combustion region and a slow combustion region, where data from the two regions is used to compute cetane values for middle distillate fluid samples using a series expansion equation.
Claims(36) 1. A method for calculating derived cetane number values comprising the steps of:
obtaining a pressure versus time combustion profile of a sample using a constant volume combustion chamber apparatus capable of yielding a combustion profile, selecting at least one data point from the profile, and calculating a derived cetane number values from a power series expansion equation expanded about the selected data points and/or arithmetic combination of the selected data points using a set of expansion coefficients. 2. The method of 3. The method of 4. The method of 5. The method of 6. The method of 7. The method of 8. The method of 9. The method of 10. The method of prior to the obtaining step, combusting a calibration sample having a known cetane number value in the constant volume combustion chamber apparatus to produce a calibration pressure versus time combustion profile, selecting at least one calibration data point from the calibration profile, computing a derived cetane number values from the power series expansion equation expanded about the selected calibration data points and/or ratios of the selected calibration data points, and adjusting expansion coefficients in the equation to minimize a difference between the known cetane number value and the derived cetane number value, where the adjusted coefficients are the set of expansion coefficients. 11. The method of DCN=C _{1a} *ID _{1} +C _{2a} *ID _{2} +C _{1b}*(ID _{1})^{2} +C _{2b}*(ID _{2})^{2} +I (I)where DCN is the derived cetane number value, ID _{1 }is the data point selected from the first region, ID_{2 }is a data point selected from the second region, C_{1a}, C_{1b}, C_{2a}, and C_{2b }are expansion coefficients and I is an intercept,
DCN=C _{1a} ID _{1} +C _{2a} ID _{2} +C _{1b}(ID _{1})^{2} +C _{2b}(ID _{2})^{2} +C _{ra} ID _{1} /ID _{2} +C _{rb}(ID _{1} /ID _{2})^{2} +I (II)where DCN is the derived cetane number value, ID _{1 }is a data point selected from the first region, ID_{2 }is a data point selected from the second region, C_{1a}, C_{1b}, C_{2a}, C_{2b}, C_{ra}, and C_{rb }are coefficients and I is the intercept, and
DCN=C _{ra} ID _{1} /ID _{2} +C _{rb}(ID _{1} /ID _{2})^{2} +I (III)where DCN is the derived cetane number value, ID _{1 }is a data point selected from the first region, ID_{2 }is a data point selected from the second region, C_{ra }and C_{rb }are coefficients and I is the intercept.12. The method of where DCN is the derived cetane number value, ID
_{i }are the data points selected from the first region, ID′_{k }are the data points selected from the second region, c_{ij }and c′_{kl }are expansion coefficients and I is the intercept, i is an integer representing a number of data points selected from the first region, j is an integer representing the number of terms in the expansion for the selected data points in the first region, k is an integer representing the number of data points selected from the second region, and l is an integer representing the number of terms in the expansion for the selected data points in the second region, andwhere DCN is the derived cetane number value, ID
_{i }are data points selected from the A region of the profile representing an ignition delay of components in the A region, ID_{k }are data points selected from the B region of the profile representing an ignition delay of components in the B region, and ID_{ii}/ID_{jj }ratios of selected data points from the A region and ID_{jj }are selected points from the B region, c_{ij}, c_{kl }and c_{iijjkk }are coefficients and I is the intercept, i is an integer representing a number of data points selected from the A region, j is an integer representing the number of terms in the expansion for the selected data points in the A region, k is an integer representing the number of data points selected from the B region, l is an integer representing the number of terms in the expansion for the selected data points in the B region, ii is an integer representing the number of data points selected from the A region, jj is an integer representing the number of data points selected from the B region, kk is an integer representing the number of terms in the expansion for the ratios of selected data points from region A to selected data points from the B region.13. The method of where DCN is the derived cetane number value, ID
_{j }are the data points selected from the i^{th }region of the profile, where each region represents components having different ignition delay time and c_{ijk }are expansion coefficients corresponding to the i^{th }region, the j^{th }point raised the k^{th }power and I is the intercept, andwhere DCN is the derived cetane number value, ID
_{j }are data points selected from the i^{th }region of the profile, where each region represents components having different ignition delay time and c_{ijk }are expansion coefficients corresponding to the i^{th }region, the j^{th }point of the i^{th }region raised the k^{th }power, ID_{ii}/ID_{jj }are ratios of data points from different regions, c_{iijjkk }are expansion coefficients corresponding to the ii^{th }data point from one region and the jj^{th }data point from a different regions raised to the kk^{th }power and I is the intercept.14. A method for calculating derived cetane number values comprising the steps of:
combusting a calibration sample having a known cetane number value in the constant volume combustion chamber apparatus to produce a calibration pressure versus time combustion profile, selecting at least one calibration data point from the calibration profile, computing a derived cetane number values from a power series expansion equation expanded about the selected calibration data points and/or ratios of the selected calibration data points, adjusting expansion coefficients in the equation to minimize a difference between the known cetane number value and the derived cetane number value to obtain a set of optimized expansion coefficients, obtaining a pressure versus time combustion profile of a sample using the constant volume combustion chamber apparatus capable of yielding a sample pressure versus time combustion profile, selecting at least one sample data point from the sample profile, and calculating a derived cetane number values from a power series expansion equation expanded about the selected sample data points and/or ratios of the selected calibration data points using the optimized expansion coefficients. 15. The method of 16. The method of 17. The method of 18. The method of 19. The method of 20. The method of 21. The method of 22. The method of DCN=C _{1a} *ID _{1} +C _{2a} a*ID _{2} +C _{1b}*(ID _{1})^{2} +C _{2b}*(ID _{2})^{2} +I (I)where DCN is the derived cetane number value, ID _{1 }is the data point selected from the first region, ID_{2 }is a data point selected from the second region, C_{1a}, C_{1b}, C_{2a}, and C_{2b }are expansion coefficients and I is an intercept,
DCN=C _{1a} ID _{1} +C _{2a} ID _{2} +C _{1b}(ID _{1})^{2} +C _{2b}(ID _{2})^{2} +C _{ra} ID _{1} /ID _{2} +C _{rb}(ID _{1} /ID _{2})^{2} +I (II)where DCN is the derived cetane number value, ID _{1 }is a data point selected from the first region, ID_{2 }is a data point selected from the second region, C_{1a}, C_{1b}, C_{2a}, C_{2b}, C_{ra}, and C_{rb }are coefficients and I is the intercept, and
DCN=C _{ra} ID _{1} /ID _{2} +C _{rb}(ID _{1} /ID _{2})^{2} +I (III)where DCN is the derived cetane number value, ID _{1 }is a data point selected from the first region, ID_{2 }is a data point selected from the second region, C_{ra }and C_{rb }are coefficients and I is the intercept.23. The method of where DCN is the derived cetane number value, ID
_{i }are the data points selected from the first region, ID′_{k }are the data points selected from the second region, c_{ij }and c′_{kl }are expansion coefficients and I is the intercept, i is an integer representing a number of data points selected from the first region, j is an integer representing the number of terms in the expansion for the selected data points in the first region, k is an integer representing the number of data points selected from the second region, and l is an integer representing the number of terms in the expansion for the selected data points in the second region, andwhere DCN is the derived cetane number value, ID
_{i }are data points selected from the A region of the profile representing an ignition delay of components in the A region, ID_{k }are data points selected from the B region of the profile representing an ignition delay of components in the B region, and ID_{ii}/ID_{jj }ratios of selected data points from the A region and ID_{jj }are selected points from the B region, c_{ij}, c_{kl }and c_{iijjkk }are coefficients and I is the intercept, i is an integer representing a number of data points selected from the A region, j is an integer representing the number of terms in the expansion for the selected data points in the A region, k is an integer representing the number of data points selected from the B region, l is an integer representing the number of terms in the expansion for the selected data points in the B region, ii is an integer representing the number of data points selected from the A region, jj is an integer representing the number of data points selected from the B region, kk is an integer representing the number of terms in the expansion for the ratios of selected data points from region A to selected data points from the B region.24. The method of where DCN is the derived cetane number value, ID
_{j }are the data points selected from the i^{th }region of the profile, where each region represents components having different ignition delay time and c_{ijk }are expansion coefficients corresponding to the i^{th }region, the j^{th }point raised the k^{th }power and I is the intercept, andwhere DCN is the derived cetane number value, ID
_{j }are data points selected from the i^{th }region of the profile, where each region represents components having different ignition delay time and c_{ijk }are expansion coefficients corresponding to the i^{th }region, the j^{th }point of the i^{th }region raised the k^{th }power, ID_{ii}/ID_{jj }are ratios of data points from different regions, c_{iijjkk }are expansion coefficients corresponding to the ii^{th }data point from one region and the jj^{th }data point from a different regions raised to the kk^{th }power and I is the intercept.25. A method for calculating derived cetane number values comprising the steps of:
2 combusting a calibration sample having a known cetane number value in the constant volume combustion chamber apparatus to produce a calibration pressure versus time combustion profile, selecting at least one data point from the calibration profile, computing a derived cetane number values from a power series expansion equation expanded about the selected data points, adjusting expansion coefficients in the equation to minimize a difference between the known cetane number value and the derived cetane number value to obtain a set of optimized expansion coefficients, burning a middle distillate sample in a constant volume combustion chamber apparatus, measuring and storing a pressure versus time combustion profile of the sample, where the profile has a first region corresponding to sample components having earlier ignition temperatures and a second region corresponding to sample components having later ignition temperatures, selecting at least one sample data point from the first region from the profile, and calculating a derived cetane number values from a power series expansion equation expanded about the selected sample data points using the optimized expansion coefficients. 26. The method of 27. The method of 28. The method of 29. The method of 30. The method of 31. The method of DCN=C _{1a} *ID _{1} +C _{2a} *ID _{2} +C _{1b}*(ID _{1})^{2} +C _{2b}*(ID _{2})^{2} +I (I)where DCN is the derived cetane number value, ID _{1 }is the data point selected from the first region, ID_{2 }is a data point selected from the second region, C_{1a}, C_{1b}, C_{2a}, and C_{2b }are expansion coefficients and I is an intercept.32. The method of DCN=C _{1a} *ID _{1} +C _{2a} *ID _{2} +C _{1b}*(ID _{1})^{2} +C _{2b}*(ID _{2})^{2} +I (I)where DCN is the derived cetane number value, ID _{1 }is the data point selected from the first region, ID_{2 }is a data point selected from the second region, C_{1a}, C_{1b}, C_{2a}, and C_{2b }are expansion coefficients and I is an intercept,
DCN=C _{1a} ID _{1} +C _{2a} ID _{2} +C _{1b}(ID _{1})^{2} +C _{2b}(ID _{2})^{2} +C _{ra} ID _{1} /ID _{2} +C _{rb}(ID _{1} /ID _{2})^{2} +I (II)where DCN is the derived cetane number value, ID _{1 }is a data point selected from the first region, ID_{2 }is a data point selected from the second region, C_{1a}, C_{1b}, C_{2a}, C_{2b}, C_{ra}, and C_{rb }are coefficients and I is the intercept, and
DCN=C _{ra} ID _{1} /ID _{2} +C _{rb}(ID _{1} /ID _{2})^{2} +I (III)where DCN is the derived cetane number value, ID _{1 }is a data point selected from the first region, ID_{2 }is a data point selected from the second region, C_{ra }and C_{rb }are coefficients and I is the intercept.33. The method of where DCN is the derived cetane number value, ID
_{i }are the data points selected from the first region, ID′_{k }are the data points selected from the second region, c_{ij }and c′_{kl }are expansion coefficients and I is the intercept, i is an integer representing a number of data points selected from the first region, j is an integer representing the number of terms in the expansion for the selected data points in the first region, k is an integer representing the number of data points selected from the second region, and l is an integer representing the number of terms in the expansion for the selected data points in the second region, andwhere DCN is the derived cetane number value, ID
_{i }are data points selected from the A region of the profile representing an ignition delay of components in the A region, ID_{k }are data points selected from the B region of the profile representing an ignition delay of components in the B region, and ID_{ii}/ID_{jj }ratios of selected data points from the A region and ID_{jj }are selected points from the B region, c_{ij}, c_{kl }and C_{iijjkk }are coefficients and I is the intercept, i is an integer representing a number of data points selected from the A region, j is an integer representing the number of terms in the expansion for the selected data points in the A region, k is an integer representing the number of data points selected from the B region, l is an integer representing the number of terms in the expansion for the selected data points in the B region, ii is an integer representing the number of data points selected from the A region, jj is an integer representing the number of data points selected from the B region, kk is an integer representing the number of terms in the expansion for the ratios of selected data points from region A to selected data points from the B region.34. The method of where DCN is the derived cetane number value, ID
_{j }are the data points selected from the i^{th }region of the profile, where each region represents components having different ignition delay time and c_{ijk }are expansion coefficients corresponding to the i^{th }region, the j^{th }point raised the k^{th }power and I is the intercept, andwhere DCN is the derived cetane number value, ID
_{j }are data points selected from the i^{th }region of the profile, where each region represents components having different ignition delay time and C_{ijk }are expansion coefficients corresponding to the i^{th }region, the j^{th }point of the i^{th }region raised the k^{th }power, ID_{ii}/ID_{jj }are ratios of data points from different regions, c_{iijjkk }are expansion coefficients corresponding to the ii^{th }data point from one region and the jj^{th }data point from a different regions raised to the kk^{th }power and I is the intercept.35. A method for determining coefficients of a series expansion equation for calculating derived cetane number values comprising the step of:
combusting a sample having a known cetane number value in a constant volume combustion chamber apparatus under controlled conditions to obtain pressure versus time combustion data, selecting at least one point from the profile, computing a derived cetane number value using the series expansion equation about the selected points with a set of initial coefficients, and adjusting coefficients of the series expansion equation so that a difference between the cetane number and the derived cetane number value is minimized. 36. A system for calculating derived cetane number values comprising:
a constant volume combustion chamber subsystem adapted to combust a sample of a middle distillate fluid/fuel in a controlled manner to produce pressure versus time data of the combustion, an analyzing subsystem adapted to select at least one point from the profile and to calculate a derived cetane number based on a series expansion equation expanded about the selected points, where the coefficients of the equation are determined by minimizing a difference between the derived cetane number value and a cetane number value of a calibration sample having a known cetane number value. Description The present application claims priority to U.S. Provisional Patent Application Ser. No. 60/868,273 filed 1 Dec. 2006 (Dec. 1, 2006). 1. Field of the Invention The present invention relates to a method and a system for calculating or measuring cetane number values of middle distillate fluids and/or fuels. More particularly, the present invention relates to a method and a system for measuring cetane number values of middle distillate fluids and/or fuels, where the method includes combusting a sample of a middle distillate fluid and/or fuel in a constant volume combustion chamber (CVCC) under conditions to produce combustion data of pressure versus time or a combustion pressure versus time profile and deriving or calculating a cetane number value from data points selected from the pressure versus time profile or from data points and data point ratios or from data point ratio. 2. Description of the Related Art Current methods and systems for measuring cetane value are based either on engine data or are based on data derived from a constant volume combustion chamber. The methods and systems utilizing constant volume combustion chamber apparatuses determine a cetane value from an equation that uses a single point from pressure versus time combustion data that corresponds to a given increase in chamber pressure after injection of a fuel sample. These methods are wrought with uncertainty for fuels having different amounts of faster burning fuel components and using apparatuses that are capable of differentiating between faster and slower burning fuel components. Thus, there is a need in the art for methods and systems for determining cetane values from constant volume combustion chamber apparatuses, especially in apparatuses capable of differentiating between faster and slower burning fluid components, where the methods and systems utilize data a pressure versus time profile in a series expansion about selected data points or selected points and ratios of the selected points or ratio of the selected points from the curve to derive improved cetane number values for middle distillate fluids and/or fuels. The present invention provides a system and method capable of determining cetane number values from a pressure v. time combustion profile of a middle distillate, where the data or profile includes a single combustion region or multiple combustion regions. The present invention also provides a system and method capable of determining cetane number values from a pressure v. time combustion profile of a middle distillate, where the data or profile includes a first region, an A region or early ignition delay region, and a second region, a B region or late ignition delay region. The A region represents fluid/fuel components having a first combustion rate and the B region represents fluid/fuel components having a second combustion rate, where the first combustion rate is faster than the second combustion rate. The present invention provides a system for computing cetane number values of middle distillate fluids and/or fuels including a constant volume combustion chamber (CVCC) subsystem having a pressure sensor, a source of an oxidizing agent, a middle distillate fluid/fuel source, a pressurizing means and a heating means. The system also includes an analyzing subsystem adapted to accumulate data during combustion of a sample in the CVCC subsystem to produce a pressure versus time data profile, and to compute a derived cetane number value from at least one data point selected from the data profile as an independent variable in a power series expansion about the selected data points or about the selected data points and ratios of the selected data points or about ratio of the selected data points. The present invention provides a system for computing cetane number values of middle distillate fluids and/or fuels including a constant volume combustion chamber (CVCC) subsystem having a pressure sensor, a source of an oxidizing agent, a middle distillate fluid/fuel source, a pressurizing means and a heating means. For combustion data profiles that include two combustion regions, an A region and a B region, the system also includes an analyzing subsystem adapted to accumulate data during combustion of a sample in the CVCC subsystem to produce pressure versus time data profile, and to compute a derived cetane number value from at least one point selected from either the A region or the B region as an independent variable in a power series expansion about the selected data points or about the selected data points and ratios of the selected data points or about ratios of the selected data points. In certain embodiments, the ratios are between selected data points from region A to selected data points from region B, i.e., ID The present invention provides a system for computing cetane number values of middle distillate fluids and/or fuels including a constant volume combustion chamber (CVCC) subsystem having a pressure sensor, a source of an oxidizing agent, a middle distillate fluid/fuel source, a pressurizing means and a heating means. For combustion data profiles that include two combustion regions, an A region and a B region, the system also includes an analyzing subsystem adapted to accumulate data during combustion of a sample in the CVCC subsystem to produce pressure versus time data profile, and to compute a derived cetane number value from at least one point selected from at least one data point selected from the A region and at least one data point selected from the B region as independent variables in a power series expansion about the selected points or about the selected data points and ratios of the selected data points from region A to the selected data points from region B or about ratios of the selected data points from region A to the selected data points from region B. The present invention also provides a method including the step of combusting a sample of a middle distillate fluid and/or fuel in a constant volume combustion chamber (CVCC) apparatus having a pressure sensor to produce combustion pressure versus time data, plottable as a pressure versus time profile. The method also includes the step of selecting at least one data point from the profile as an independent variable for a power series expansion about the selected point or points. The method also includes the step of computing a derived cetane number value utilizing the selected point or points as independent variables in a power series expansion about the selected points, where the derived cetane number value has a greater accuracy than a cetane number value calculated from a non-power series expansion using only a specific point from the same data. The method can also include the step of calibrating coefficients of the expansion equation using sample with known cetane number values. The present invention also provides a method including the step of combusting a sample of a middle distillate fluid and/or fuel in a constant volume combustion chamber (CVCC) apparatus having a pressure sensor to produce combustion pressure versus time data, plottable as a pressure versus time profile. For data profiles that include a first region, the A region, and a second region, the B region, the method also includes the step of selecting at least one data point from the profile as the independent variable for a power series expansion about the selected point or points. The selected points can include one or more points from either the first region of the profile corresponding to ignition of faster burning components of the fluid/fuel or the second region of the profile corresponding to ignition of slower burning components of the fluid/fuel or both. The method also includes the step of computing a derived cetane number value utilizing the selected point or points as independent variables in a power series expansion about the selected points, where the derived cetane number value has a greater accuracy than a cetane number value calculated from a non-power series expansion using only a specific point from the same data. The method can also include the step of calibrating coefficients of the expansion equation using sample with known cetane number values. The present invention also provides a method including the step of combusting a sample of a middle distillate fluid and/or fuel in a constant volume combustion chamber (CVCC) apparatus having a pressure sensor to produce combustion pressure versus time data, plottable as a pressure versus time profile. For data profiles that include a first region, the A region, and a second region, the B region, the method also includes the step of selecting at least one point from the A region and at least one point from the B region. The method also includes the step of deriving a cetane number value from an equation using the least one point from the A region and the at least one point from the B region as independent variables in a power series expansion about the point to compute a derived cetane number value that is closer to an actual cetane number value of the sample as compared to computing a cetane number value from a non-power series expansion using only a specific point from the same data. The method can also include the step of calibrating coefficients of the expansion equation using sample with known cetane number values. The represent invention also provide a method for determining coefficients of a series expansion equation for calculating derived cetane number values comprising the step of combusting a sample having a known cetane number value in a constant volume combustion chamber apparatus under controlled conditions to obtain pressure versus time combustion data. Next, at least one point from the profile is selected and a derived cetane number value using the series expansion equation about the selected points with a set of initial coefficients is computed or calculated. Next, the coefficients of the series expansion equation are adjusted so that a difference between the cetane number and the derived cetane number value is minimized. The invention can be better understood with reference to the following detailed description together with the appended illustrative drawings in which like elements are numbered the same: The inventor has found that a new method can be formulated for determining derived cetane number values of middle distillates from combustion data derived from a constant volume combustion chamber (CVCC) apparatus. The inventor has found that superior derived cetane number values can be calculated using a series expansion equation, expanded about one data point or a plurality of data points from a pressure versus time data collected when a middle distillate fluid and/or fuel sample is burned in the CVCC apparatus. The inventor has found that superior cetane number values can be obtained using the CVCC capable of yielding a pressure/time profile including multiple combustion regions. For example, certain pressure/time profiles include an A region and a B region produce, where the A region represents fuel components with shorter (early) ignition delay times (faster burning components) and the B region represents fuel components with longer (later) ignition delay times (slower burning components). The inventor has found cetane number calculations using at least one data point selected from each combustion region as the independent variables yield superior derived cetane number values than calculations based on only a single, specific pressure/time data point. For example, profiles having an A region and a B region, cetane number values derived from equations using at least one point from the A region and at least one data point selected from the B region yield superior derived cetane number values than calculations based on only a single, specific pressure/time data point. The present invention broadly relates to a system for determining or calculating cetane number values for known and/or unknown middle distillate fluid and/or fuel samples. The system includes a combustion subsystem comprising a constant volume combustion chamber (CVCC) apparatus for obtaining pressure versus time data from the combustion of a known or unknown middle distillate fluid and/or fuel sample. The system also includes an analyzing subsystem for selecting at least one data point as an independent variable int an expansion equation capable of calculating a derived cetane number value from the at least one selected point as the independent variable in the equation. For data that has multiple regions, at least one data point is selected from each region as independent variables in calculating a derived cetane number value. The calculation can also include ratios of data points from each region. In certain embodiments, the ratios are between data points from the regions corresponding to earlier ignition components and later ignition components. In other embodiments, the calculation use just the ratios of the selected data points. For data that has A and B regions, at least one point is selected from the A region and at least one point is selected from the B region as independent variables in calculating a derived cetane number value. In certain embodiments, the calculation also utilize ratios of selected data points as additional independent variable. In other embodiments, the calculation uses just ratios of selected points. In other embodiments, the ratios are selected data points from region A to selected data points from region B. i.e., ID The present invention also broadly relates to a method including the step of combusting a sample of a middle distillate fluid and/or fuel in a constant volume combustion chamber (CVCC) apparatus having a pressure sensor and/or a temperature sensor to produce combustion pressure versus time data, plottable as a pressure versus time profile. The method also includes the step of selecting at least one data point. The method also includes the step of calculating or computing a derived cetane number value utilizing the at least one data point as independent variable in an expansion equation. For profiles that include multiple regions, the selecting step includes selecting at least one point from each region. For profiles that include A and B regions, the selecting step includes selecting at least one data point from the A region and the at least one data point from the B region as independent variables, where the A region corresponds to the ignition of faster burning components of the fluid/fuel and the B region corresponds to the ignition of slower burning components of the fluid/fuel. The method also includes the step of computing a derived cetane number value utilizing the selected data points, utilizing the selected data points and ratios of the selected data points, or utilizing ratios of the selected data points from the regions as independent variables in an expansion equation. The method can also include the step of calibrating coefficients of the expansion equation using sample with known cetane number values. Suitable middle distillate fluids and/or fuels includes, without limitation, any hydrocarbon fluid or fuel that has a middle boiling point in the context of refined hydrocarbons derived from crude oil or bio-material fluids or fuels or synthetic fluids or fuels with boiling points in the range of middle boiling point refined hydrocarbons, or mixtures or combinations thereof. Non-limiting exemplary examples of such fluids include diesel fuels, diesel fuels with cetane improving additives, jet fuels, bio-diesel fuels, kerosenes, or the like. Although generally middle distillates are hydrocarbons that include primarily gas oil and aviation jet fuel (or high-grade kerosene), the inventors use it here to refer not only to the distillates derived from the processing of crude oil, but also fuels derived from bio-materials, so called bio-diesels, and fuels derived from Fischer-Tropsch catalytic polymerization of hydrogen/carbon monoxide mixture, so called syn-gas, into hydrocarbon fuels with in the middle distillate range. Gas oil is increasingly used as an industrial fuel, displacing fuel oil because of environmental concerns. It is also used as a fuel for buses, lorries, and taxis. Jet fuel is commonly used as an aviation fuel and also as a domestic fuel for heating purposes. The system and method of this invention utilize data derived from a constant volume combustion chamber (CVCC) apparatus to compute a derived cetane number value for a middle distillate fluid/fuel, where a middle distillate fluid/fuel sample is combusted at an elevated temperature and pressure. The sample is injected into the CVCC apparatus at a predetermined pressure and temperature. After injection, a pressure in the chamber is measured as a function of time after injection until combustion is complete. In prior art methods, a single data point from the pressure/time data representing an ignition delay was selected to be used in an equation to compute or calculate a derived cetaine number (DCN) that would correspond to a cetane number (CN) measured using a special internal combustion engine. However, with the advent of new fuel mixtures, the derived cetane number values have shown mark deviations from the actual cetane number values. Using newer CVCC apparatuses to combust samples, pressure/time profiles are produced that show a single region or multiple regions. In certain samples, the pressure/time profile has only a single region. In other samples, the profile shows a main region having a shoulder. In other samples, the profile has two distinct regions. The first region or shoulder evidences early burning components, while the main profile or second region evidence late burning components. The first region, sometimes referred to herein as the A region, represents fluid/fuel components that have a shorter ignition delay (start burning earlier), and the second region, sometimes referred to herein as the B region, represents fluid/fuel components that have a longer ignition delay (start burning later). Because fluids/fuels generally give rise to a two region pressure/time profile when tested in newer CVCCs, the DCN values show considerable and inconsistent disagreement with their corresponding actual CN values. The present method significantly reduces these variances, by using at least one data point from each region, at least one data point from each region and ratios of the data points from different regions or ratios of data points from different regions of the pressure/time profile in a series expansion equation to generate DCN values having smaller variances from their corresponding actual CN values, where the expansion is relative to the selected data points, the selected points and ratios, or ratios as independent variables in the equation. Referring now to The apparatus Once a samples has been combusted in an apparatus of In one embodiment, a derived cetane number is calculated from second order equation (I): where ID In one embodiment, a derived cetane number is calculated from second order equation (II):
where ID In one embodiment, a derived cetane number is calculated from second order equation (III): where ID In another embodiment, the cetane number is calculated from a more generalized equation (IV):
where ID In another embodiment, the cetane number is calculated from a more generalized equation (V):
where ID In another embodiment, the cetane number is calculated from an even more generalized equation (VI):
where ID In another embodiment, the cetane number is calculated from an even more generalized equation (VII):
where ID In the current ASTM standard method D 6890-03a for determining DCN values using a conventional CVCC system, the method includes a plot of the nozzle movement associated with the injection of a sample in millisecond and a plot of the combustion profile of the injected sample with the time axis in milliseconds (ms) and the pressure axis in mega Pascals or Bar. The method then requires the selection of an ignition delay point were the pressure rises to a value of 0.02 mPa above the initial pressure. This point is then used in a standard equation to compute a derived cetane number (DCN). The data derived from these conventional CVCC systems generally show a combustion curve having only a single region, i.e., after ignition, the curve simply rises to a plateau. Referring now to Referring now to The pressure waves or profiles using a modern injector CVCC apparatus typically are different from those obtained using conventional CVCC apparatuses in general use today, which generate profiles typically having only a combustion curve having a single profile or region, i.e., the curve is not capable of discriminating between early burning components and late burning components. The new CVCC apparatus such as the apparatus of In certain embodiments, low chamber temperatures are used to improve the differentiation between derived cetane number values for samples that would give essentially the DCN value using the conventional ASTM method. The obtained pressure curves or profiles are sensitive to a volume of the injected sample so care should be exercised in sample injection. Additionally, stable stoichiometry (size of sample injected) is important for stable pressure data. The present invention is based on the inventor's recognition that more than one pressure/time data point (sometimes referred to herein as an ID measurement) along the pressure curve is required to differentiate between hydrocarbon fuels, cetane-improved fuels and bio-diesels and to generate DCN values for unknown middle distillate fluids/fuels that more closing match their corresponding CN values. The inventor has found that equations using only a single point ID measurement do not give satisfactory DCN determination for all types of samples. The DCN values obtained from these equations show large and unpredictable DNC value variances relative to their corresponding CN values. The present invention based on at least two point ID measurements, one from each region of the profile, yields DCN values that are better predictors of the corresponding CN values, i.e., the DCN values are closer to the CN values. Table I tabulates CN and DCN values based on a single data point selected from the pressure/time curves for the tabulated samples.
The data clearly demonstrate that the classical method for calculating DCN values yields DCN values having large variances or deviations from their corresponding CN values. Table II tabulates CN and DCN values based on a single data point selected from the pressure/time curves for the tabulated samples in a power series expansion based on the single point, where the expansion is terminated at the second order.
The table clearly demonstrates that including a second order term for calculating DCN values even in the standard fit model yields DCN values having smaller deviations or variances for most of the samples compared to actual CN values. Because this new calculation reduces the variance between the DCN values and the CN values, the present invention also includes the use of a second order term and/or higher order terms in the classical single ID linear fit method as set forth in ASTM standard method D 6890-03a. Table III tabulates CN and DCN values based on a power series expansion based on the single point ID
The table clearly demonstrates that the DCN values derived from the present equations yield DCN values with even smaller deviations from their corresponding CN values. Table IV tabulates CN and DCN values based a power series expansion based on the single point ID It should be recognized that the analyzing part of the system of this invention are designed to be coded into a software routine that will run on computer components of the analyzer of the CVCC. Thus, the components of the system and the steps of the method that required computations or calculations are designed to occur in software routines encoding the component or method step. Thus, equations (I-VII) are designed to be implemented on a computer, where the software in encoded so as to take a set of selected data points from a pressure versus time profile and calculate a derived cetane number value based on a software implementation of one or more of the equations (I-VII).
The table clearly demonstrates that the DCN values derived from the present equations yield DCN values with even smaller deviations from their corresponding CN values. All references cited herein are incorporated by reference. Although the invention has been disclosed with reference to its preferred embodiments, from reading this description those of skill in the art may appreciate changes and modification that may be made which do not depart from the scope and spirit of the invention as described above and claimed hereafter. Referenced by
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